Process of treating smokeless powder



Patented Mar. 10, 1936 UNITED STATES PROCESS OF TREATING SMOKELESS POWDER Richard G. Woodbridge, Wilmington, Del., as-

slgnor to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware No Drawing. Application July 1, 1933,

11 Claims.

The object of my invention is to restore the chemical stability of nitrocellulose smokeless powders which have undergone deterioration during storage and at the same time to conserve the ballistic qualities of the powder. My invention,

while not limited to such, is particularly applicable to smokeless powder of the so-called Pyro type, that is, powder made from nitrocellulose with a nitrogen content of 12.50 to 12.70% having a solubility in ether-alcohol mixture in excess of 95% of which more than one billion pounds were made during the World War in the United States for the use of the Allied Governments.

This application is a continuation in part of, my application, Serial No. 643,895, filed Nov. 22, 1932.

It is well known that smokeless powder deteriorates during storage. As more than 14 years have elapsed since the end of the World War the Pyro cannon powder made during the stress of war time conditions is approaching the end. of its useful life. This is particularly true since Pyro cannon powder of war time manufacture was for the greater part water-dried, that is, steeped in hot water in order to remove to the desired degrees the volatile solvents, ether and alcohol, used in its manufacture.-

Up to the present time deteriorated nitrocellulose smokeless powders of the Pyro type have been reworked by a process involving pulverizing the powder grains under water .by means of a heavy wheel mill and subjecting the finely divided material to a repurification treatment similar to that employed in the regular poaching treatment of the original nitrocellulose.

This process of reworking powder is described on pages 62 and 63 of Military Explosives, 1919 (revised edition), published .by the Government Printing Ofiice, from which the following quo- 40 tation is taken:

The reworked Pyro at this stage is very dissimilar to the regular Pyro and presents many obstacles from the .manufacturing standpoint. It is yellowishincolor, does not respond readily cake it forms on thesc'r'een, and offers many problems in chemical analysis, especially when deterthe regular Pyro, is more friable'and is in fact to the purification treatment is, diflicultof manipulation in the wringers on account of the dense drating presses the utmost care must be exercised, for on different occasions the careless manipulap tion of the pressure valves has resultedinjthe' b1owin g'up'of the press. with its attendantfire and loss of life. The dehydrated .blockftinlike Serial No. 678,731

so lacking in cohesiveness that it can not be put in the block breaker prior to the mixing operation.

Its photomicrograph also shows certain definite differences, one of the most striking being the reduction in the number and size of the fibers, thus indicating the action of the previous colloiding operation.

Smokeless powder reworked by the above described process has a relatively limited storage life because the process does not completely remove the deteriorated products. For that reason the reworked powder is usually assigned for practice use.

The object of my invention is to restore the chemical stability of the deteriorated powder 15 while still retaining the powder grains in their original form, and thereby prolong its useful life. Another object of my invention is to conserve the ballistic properties of the powder while restoring its chemical stability. A still further ob- 20 ject of my invention is to avoid the expense of grinding and reworking deteriorated nitrocellulose smokeless powder and to further avoid the accompanying hazards of manufacture of new powder therefrom.

When Pyro nitrocellulose powder grains of the multiperforatedtype are extracted with hot ethyl alcohol according to the process described in United States Patent 1,439,656 granted to me under date of December '19, 1922, considerable 0 swelling of the powder grains takes place. This swelling, amounting to approximately 15 to 20% increase in the dimensions of the grains, is accompanied by a softening of the entire grain, that is, of the colloid. This process has been ex- 35 tensively used in the lacquer industry and the softened condition of the grains facilitates their 1 solution in varioussolvents. If-the extracted powder grains are redried to-removethe excess alcohol, the grains, besides being devoid of di- 40 of cracks; These cracks in the larger 'sized'p'ow-' der grains, such as for the 155. In/ m gun, are made up in part of radial cracks extending fromithe 45,

perforations and cracks or splits in thesiz es of' the grains. These cracked and split powder grains "give a decided increase inpressure abcpve,that. given by thefuntreatedpowder, whichincrease may exceed the maximum allowable pressure. 50 I believe that thisjcracking Or splitting of the powder grains is largelygif not entirely, due to strains andst'resses'seflnp, in ,thejswelling of the colloid the alcohol extraction, process. This difficult'y is eliminated in my process.

In the extraction of Pyro cannon powder for use in the lacquer industry the'hard dried powder grains are extracted with hot alcohol at the start or if cold alcohol is used, the temperature is quickly raised to boiling. This causes a very rapid swelling of the powder grains causing the colloid to rupture. I have found that this can be largely, if not entirely, eliminated if the powder grains are allowed to soak, preferably about from 8 to 16 hours, at room temperature in the ethyl alcohol used for extracting before heating the alcohol up to the boiling point. This pretreatment of the grains before extraction permits the swelling of the grains to take place gradually and with little or no rupturing of the colloid. It should be understood that the pretreatment may be extended beyond the 16 hours for the larger grains and that a shorter treatment than 8 hours may be used for the smaller grains. I have further found that it is desirable during the extraction process with alcohol and the redrying treatment of the powder grains to avoid subjecting the same to sudden changes of temperature.

One embodiment of my invention is more fully ratus with reflux condensers to prevent loss of alcohol. The powder grains are subjectedto repeated extractions of two hours each preferably using fresh hot alcohol for each extraction in order to remove as completely as possible the diphenylamine and derivatives thereof and certain deteriorated products from the powder. The extraction time will vary according to the size of the powder grains and to the condition of the powder. For powder of the 155 m/m size ten extractions of two hours each are usually sulficient to reduce the remaining diphenylamine and derivatives to less than 0.02%. extractions required by a particularlot of powder can be readily found by determining the amount of remaining diphenylamine at hourly intervals during extraction. Once this is deter- The number of that if the swollen grains are not permitted to shrink nor the surface of the grains to harden that the fresh diphenylamine in alcoholic solution penetrates readily to all portions of the grains.

This is shown by the following results of analysis obtained on portions of 155 m/m powder of the Pyro type subjected to the above described treatment:-

Per cent diphenylamine content Exterior portions of outer and inner webs 0.65 Interior portions of outer and inner webs 0.53 Whole grains 0.61

The amount of fresh diphenylamine which I put back in the powder grains will be in the neighborhood of 0.50% in order that the potential of the rejuvenated powder will not vary materially from that of the original powder. However, I do not limit myself to any particular amount as in some cases it may be desirable to put back in the powder less and in some cases more diphenylamine than that originally present. A convenient strength of alcoholic diphenylamine solution is about 0.98% by weight and a convenient ratio of solution to powder is about 2 to 1.

The treatment of the extracted powder grains with fresh alcohol and fresh diphenylamine may be done in several alcoholic solutions of diphenylamine containing increasing amounts of diphenylamine.

In addition to restoring fresh diphenylamine to the powder there may be added in the alcohol small amounts of a plasticizer for nitrocellulose such as dinitrotoluol for the purpose of colloiding the nitrocellulose and further extending the stability life of the powder.

The restabilized powder grains are drained to remove excess alcoholic diphenylamine solution, subjected to solvent recovery treatment followed by drying in air or steeping in hot water in order to reduce the residual solvent to the desired point. I have found that the residual solvent may be advantageouslyreduced below the amount originally present in the powder because of the slight increase in web thickness caused by the treatment.

mined for a particular granulation and addition- This is illustrated by the following data on 155 al time allowed as a margin of safety, a more or m/m powder:-

' Moisture Total vola- Residual Muzzle Mean resfir g tiles :66??? solvent 2253 velocity sur percent Doreen; percent l. s. ibs./sq. in.

Untreated powder .0550" 5.48 1.43% 4.05% -25 lbs 2422 29,030 Rei uvlenated powder, Bam- .0608" 4.07 o 1.24% 3.73% 26lbs.201. 2420 29,050

pa Rel uvgnated powder, Sam- .0609" 4.20% 1. 26% 2. 94% 25 lbs 2404 29,180

less standard time may be set up for the treatment of that particular granulation. The alcohol used for extracting a fresh batch of powder can be used to extract another batch of powder, etc., depending on the condition of the powder being extracted.

After the final extraction has been completed the excess alcohol is allowed to drain from the powder and while the powder grains are still in a swollen state'and soft they are treated with a hot alcoholic solution of new diphenylamine for about 24 hours in order to thoroughly impregnate the powder with stabilizer. I have found Although the total volatile and residual solvent contents of Sample 1 of rejuvenated powder were well belowthose of the untreated powder, the weight of charge required was .1 lb. 2 oz. more, due probably to the increase in web of the rejuvenated powder. By reducing the total volatile and residual solvent contents decidedly below those of the untreated powder, the weight of charge required for, Sample 2 was brought down to that of the untreated powder.

As proof that the chemical stability of the powder treated by my process is restored I give below the results of stability tests on 75 m/m water dried Pyro cannon powder of war time manufacture treated according to nay-process.

German Total test at amount of Amount of 135 C Surveillance altered and unaltered Minutes for test at unaltered diphenylturning of 65.5 C. diphenylamine Standard Days for amine present ethyl red fumes present Violet Paper Untreated powder Tested in 1924.-. 0.57% 39% 70 366,399,399 Tested in 1929 after years at 30 0. 60 160,195

Note: Removed from storage at 30 C. on account of red fumes after 6 years 7 months and 14 days at this temperature.

Treated powder Tested in 1924. 0.66% o. 66% 135' 585, 662, 686 Tested in 1929 after 5 years at Note: Still in storage at 30 0.

It should be understood that the above powder before treatment was approximately six years old and had been stored at atmospheric temperature since manufactured and that about onethird of 'the diphenylamine had been consumed by conversion into nitro derivatives thereof. A portion of the untreated powder, after six years of storage at atmospheric temperature was placed in storage at 30 C. but decomposed after 6 years 7 months at this temperature to the point of giving oif red fumes. On the other hand portions of the treated powder have shown by results of the German test at 135 C. and the surveillance test at 65.5 C. a degree of chemical stability approximately that of newly made Pyro cannon powder which renewed stability is substantiated by continued good condition of the powder at 30 C. The treatment has therefore added many years of useful service life to the powder, that is, the powder has been rejuvenated.

This rejuvenating process may be applied to the powder at any time during its storage life and preferably before the powder has consumed all of its original diphenylamine content. process is particularly applicable to Pyro cannon powder which has been subjected to storage under water during which a considerable amount of its normal residual solvent content may have been removed. Treatment of such powder by my process not only puts back into the powder fresh diphenylamine but also fresh alcohol to replace that lost during storage under water.

In certain cases where the decomposition of the powder has proceeded to a point at which the acidity of the powder has been materially increased, it may be desirable to neutralize this acidity by the use of alkalies, preferably carbonates. This may be done during the extraction process or prior thereto by steeping in alkaline water followed by washing in fresh water.

The ethyl alcohol used both for the extraction and the replacement of diphenylamine in the rejuvenating treatment may be denatured ethyl alcohol, Formula #2-B containing one-half gallon of benzol per 100 gallons of ethyl alcohol, or denatured ethyl alcohol of other suitable formula. A small amount of ether may be added to the alcohol during the rejuvenating treatment.

It should be understood that the extraction good condition as regards stability after 8% years process with alcohol may be varied considerably from the preferred treatment previously described. For example, a continuous extraction process may be employed in which the powder grains are so placed in a container that they may be heated by hot solvent vapor and extracted by the warm solvent that passes down over them in a continuous manner.

While my process is particularly applicable to the rejuvenation of Pyro cannon powder, it is also applicable to the rejuvenation of Pyro rifle powder and to the rejuvenation of any subdivision of 'these orother nitrocellulose powder obtained by grinding or cracking of the same into smaller granulations whether the same be intended for use as a shotgun powder or other propellent purpose.

It is also applicable to other types of nitrocellulose powder than Pyro cannon powder, such as nitrocellulose powders made from a mixture of nitrocellulose soluble in ether-alcohol mixture and nitrocellulose insoluble in such mixture. My process is also applicable to nitrocellulose powders of the surface treated type containing dinitrotoluene, dimethyldiphenylurea or other surface impregnating materials which together with any derivatives thereof can be readily extracted by treatment with hot alcohol at the same time that the diphenylamine and derivatives thereof are extracted. In the latter case the rejuvenation treatment with fresh alcohol and fresh diphenylamine is followed by a surface coating or impregnating treatment with dinitrotoluol or dimethyldiphenylurea in order to restore to the powder its original progressive burning characteristics.

As many apparently widely different embodiments of this invention may be made without departing from the spirit thereof, it is to be understood that I do not limit myself to the foregoing examples or descriptions except as indicated in the following patent claims.

I claim:

1. The. process of rejuvenating powder of the surface coated or surface impregnated type comprising extracting the coating material, diphenylamine and derivatives thereof with ethyl alcohol, by suspending the grains in the alcohol at substantially room temperature and subjecting the suspension to gradual rise in temperature, restoring the diphenylamine and coating material and redrying the powder.

2. The process of restoring the chemical stability of nitrocellulose smokeless powder which has undergone deterioration during storage, while retaining the powder grains substantially in their' original form, which comprises swelling the grains gradually to avoid rupture of the colloid by soaking the powder grains in a solvent, gradually heating the powder in a solvent to the boiling point so as to avoid subjecting the grains of powder to a sudden change of temperature, extracting the powder to remove the stabilizer, removing the solvent, and impregnating the pownitrocellulose Pat It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

der with new stabilizing material by treating the powder grains while in aswollen state with a hot solvent solution of fresh stabilizing material.

4. The process of restoring the chemical stability of nitrocellulose smokeless powder which has undergone deterioration during storage, while retaining the powder grains in substantially their original form, which comprises swelling the grains gradually to avoid rupture of the colloid, gradually heating the powder in alcohol to the boiling point so as to avoid subjecting the grains of powder to a sudden change of temperature, extracting the powder to remove the old stabilizer, repeating the extraction, and impregnating the powder with new stabilizing material by treating the powder grains while in a swollen state with a'hot alcoholic solution of fresh stabilizing material for approximately twenty-four hours.

5. The process of restoring the chemical stabilityof nitrocellulose smokeless powder which has undergone deterioration during storage, while retaining the powder grains substantially in their original form, which comprises swelling the grains gradually to avoid rupture of the colloid, heating the grains in alcoholic solution to the boiling 'point of the alcohol, extracting the powder to remove the stabilizer, and impregnating the powder with fresh stabilizing material.

6. The process of restoring the chemical stability of nitrocellulose smokeless powder which has undergone deterioration during storage, while retaining the powder grains in substantially their original form, which comprises swelling the grains gradually to avoid rupture of the colloid by soaking the powder grains in alcohol, gradually heat ing the powder in alcohol to the boiling point so as to avoid subjecting the grains of powder to a sudden change of temperature, extracting the powder to remove the stabilizer, removing the alcohol, and impregnating the powder with new stabilizing material by treating the powder'grains while in a swollen state with a hot alcoholic solution of fresh stabilizing material.

7. The process of restoring the chemical stability of nitrocellulose smokeless powder which has undergone deterioration during storage, while retaining the powder grains in substantially their original form, which comprises swelling the grains gradually to avoid rupture of the colloid by soaking the powder grains in ethyl alcohol at room temperature, gradually heating the powder in alcchol to the boiling point so as to avoid subjecting the grains of powder to a sudden change of temperature, extracting the powder with alcohol to remove the old stabilizer, repeating the extraction with fresh alcohol, removing the alcohol, impregnating the powder with new stabilizing material by treating the powder grains while in a swollen state with a hot alcoholic solution of fresh stabilizing material for approximately twentyfour hours.

8. The process of restoring the chemical stability of nitrocellulose smokeless powder which has undergone deterioration during storage, while retaining the powder grains in substantially their original form, which comprises swelling the grains gradually to avoid rupture of the colloid by soaking the powder grains in ethyl alcohol for from' 8 to 16 hours at room temperature, gradually heating the powder in alcohol to the boiling point so as to avoid subjecting the grains of powder to a sudden change of temperature, extracting the powder with alcohol to remove the diphenylamine, repeating the extraction with fresh alcohol, removing the alcohol, impregnating the powder with fresh diphenylamine by treating the powder grains while in a swollen state with a hot alcoholic solution of fresh diphenylamine for approximately twenty-four hours.

9. The process of restoring the chemical stability of Pyro smokeless powder which has undergone deterioration during storage, while retaining the powder grains in substantially their original form, which comprises swelling the grains gradually to avoid rupture of the.co1loid by soaking the powder grains in ethyl alcohol for from 8 to 16 hours gradually heating the powder in ethyl alcohol to the boiling point so as to avoid subjecting the grains of powder to a sudden change of temperature, extracting the powder with alcohol to remove the diphenylamine, repeating the extraction with fresh alcohol, removing the alcohol, impregnating the powder with new stabilizing material by treating the powder grains while in a swollen state with a hot alcoholic solution of fresh diphenylamine for approximately twenty-four hours.

10. The process of claim 2 in which small amounts of a plasticizer for nitrocellulose are added for the purpose of colloiding the nitrocellulose and further extending the stability-life of the powder.

11. The process of claim 2 in which small amounts of dinitrotoluol are added for the purpose of colloiding the nitrocellulose andfurther extending the stability-life of the powder.

RICHARD G. WOODBRIDGE.

CERTIFICATE OF CORRECTION.

ent No. 2,035,217.

March 10, 1.936.

RICHARD G. WOODBRIDGE.

column, line 26, for "0.98%" read 0.8%; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 12th day of May, A. D. 1936.

Leslie Frazer Acting Commissioner of'Patents.

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